DurableSubscriptionTest is not thorough enough

Details

Description

DurableSubscriptionTest is not thorough enough.

For example, testResubscribeWithChangedSelector() does not check that upon resubscription the previously existing subscriptions queue is deleted before being used by the new subscription. As a result, QPID-2418 is not detected by the test.

Also, testUnsubscribe() does not check that the queue backing the durable subscription is actually removed upon unsubscription (which in this case it is, as due to lack of selector usage it is not affected by the above noted defect).